Conventionally, there has been known an assembled battery provided with a plurality of prismatic batteries (see JP-A-2011-34775). To be more specific, the assembled battery includes a plurality of prismatic batteries arranged in a row in one direction, and spacers arranged between the prismatic batteries. The prismatic battery includes: a power generating element formed by layering a foil-like positive electrode and a foil-like negative electrode; and a prismatic case where the power generating element is housed.
In the prismatic battery of the assembled battery, when charging and discharging are repeated, expansion and shrinkage of the power generating element are repeated. Further, due to the repetition of charging and discharging, the positive electrode and the negative electrode of the power generating element deteriorate. Due to such deterioration of the positive electrode and the negative electrode, a reaction byproduct (a film, a gas or the like) is deposited on surfaces of the positive electrode and the negative electrode and hence, the power generating element expands.
Concerning the rigidity of the prismatic case, in a surface which faces a direction that the prismatic batteries are arranged (that is, a surface which opposedly faces the spacer), rigidity of a center portion of the surface is particularly small. Thus, in the prismatic battery, when the power generating element repeats expansion and shrinkage thereof due to the repetition of charging and discharging, a reaction force from the case against the expansion of the power generating element is small. Accordingly, a reaction force from the case against expansion of the power generating element becomes non-uniform between the center portion and other portions of the surface of the case and hence, in the power generating element, the positive electrode and the negative electrode which form the power generating element are partially displaced. As a result, a distance between the positive electrode and the negative electrode layered in the power generating element becomes non-uniform locally.
When a distance between the positive electrode and the negative electrode becomes non-uniform locally in the power generating element, the degree of progress of the deterioration of the positive electrode and the negative electrode when charging and discharging are repeated becomes non-uniform locally. In this case, a reaction in the power generating element at the time of charging and discharging becomes non-uniform thus lowering a capacity and an output of the power generating element.